Extract the zip file into a folder on your computer. Once extracted, drag the file to the root directory of your Sansa Clip.

Disconnect the Sansa Clip and let it restart. The firmware update will now begin. Once it finally finishes doing its update, it will boot back up. Once its back to the main menu, head to "Settings" > "System Info", and verify the "Version" is now 01.01.20A.